This invention is directed generally to the sensing or detection arts, more particularly to novel and improved apparatus for sensing the passage of discrete articles through a given portion of a given path of travel. While the invention may find a plurality of useful applications, the disclosure will be facilitated by addressing the specific problem of accurately detecting the passage of individual seeds through a seed planting tube, conduit or chute of a seed planting apparatus, so that the number of seeds planted may be accurately counted.
As is well known, a farmer engaged in mechanized planting of various seeds utilizes a planting machine pulled behind a tractor. Such planting machines usually include a plurality of spaced apart planting units which are supplied with seeds from one or more hoppers or containers so that a plurality of rows of seeds may be planted at one time. Numerous useful monitoring systems have been disclosed in the prior art for maintaining a count of the seeds planted by such a planting machine and providing useful indications or read-outs such as seed population and the like to an operator. However, it will be recognized that the accuracy of such counting, computing and indicating apparatus is dependent upon the accuracy and reliability of the sensing device or devices utilized therewith. In practice, a single sensing device is associated with each of the seed planting conduits or chutes of the multi-row planting machine, to provide an output signal in response to the passage of each seed therethrough.
Over the course of development of such seed sensors, a number of approaches have been developed. The earliest of these approaches utilized a sensitive mechanical switch having an actuator member placed in the flow path of the seeds within the seed chute or conduit. Such sensor devices are shown, for example, in U.S. Pat. No. 2,907,015 to Young; in U.S. Pat. No. 3,527,928 to Ryder et al; and in U.S. Pat. No. 3,632,918 to Anson et al. As the seed sensing art developed further, photosensitive devices were found to be somewhat more reliable in operation than the mechanical switches, whereby a number of sensors were constructed utilizing a light beam and a photosensitive device in optical alignment at opposite sides of the seed chute or conduit. In this arrangement, the passage of a seed through the conduit and between the light beam and photosensitive device produced a characteristic output signal which could be monitored to maintain a count of the seeds passing through that seed planting tube or chute. Such devices are shown, for example, in U.S. Pat. No. 3,537,091 to Shenkenburg; in U.S. Pat. No. 3,723,989 to Fathauer; and in U.S. Pat. No. 3,974,377 to Steffen. These latter photosensitive types of seed sensing devices are the type most widely used in the art today. However, a number of problems have been encountered with such photosensitive devices. The foregoing Fathauer and Steffen patents offer solutions to some of these problems, without abandoning the use of a photosensitive sensing device. Specifically, it is well known that dirt, dust or the like may enter the seed planting conduit or tube over a period of time, and both obscure the light source and interfere with the reception of the light beam by the photosensitive device. Consequently, such dirt or dust can inhibit proper operation of this type of sensor, causing a failure to detect the passage of seeds. Moreover, it has become a common practice for farmers to utilize seeds which have been pretreated or coated with various insecticides or liquid fertilizers. Such substances often are deposited in the tube or conduit as numerous seeds pass therethrough, thereby causing a build up of material on the inner walls of the seed conduit or tube. Such a build up of relatively viscous material will similarly obscure the light source and/or photosensitive device, thereby interfering with the detection of seeds.
In addition to the aforementioned improvements of Fathauer and Steffen in photosensitive sensing systems, intended to overcome these problems, an alternative arrangement in the form of an ultrasonic sensing apparatus has been devised, as disclosed in U.S. Pat. No. 3,881,353 to Fathauer.
While the foregoing seed sensor devices have made considerable advances in overcoming the previously mentioned problems, at least one additional problem stills remains. It will be recognized that in the mechanized planting of seeds, relatively large numbers of seeds, ie. large seed populations, are planted in relatively short periods of time. This necessitates seeds being discharged from each seed planting unit or chute in rapid succession as the seed planting machine moves over the field to be planted. Moreover, planting machines commonly in use generally are equipped with eight to sixteen such planting units, and in some cases as many as twenty-four. Accordingly, multiplexing methods have been utilized to accommodate a corresponding number of seed sensors. However, such multiplexing must be accomplished at relatively high speed if a running count is to be obtained from all of the seed sensors simultaneously. This in turn requires that the seed sensing device utilized have a very fast response time, so that it produces an output signal within a very short time of the passage of a seed. Moreover, the seed sensing device utilized must also exhibit a fast recovery time in order to produce a separate and discrete output signal in response to each of the seeds passing through its associated conduit. A related problem is that of distinguishing between two or more seeds which pass the sensor in relatively close proximity so as to maintain an accurate seed count. The foregoing problems may collectively be characterized as a problem of achieving adequate resolution in the sensing device.